Secrecy system



JUN 28 1927" L. ESPENSCHIED SECRECY SYSTEM Original Filed March 5 1921jvwantoz Patented June 28,

UNITED STATES l .PATENT vori-ica LLOYD nsrmrscnmn, or oumannw Yoan,.AssrGNoa 'ro Annalen: 'rnnnrnomi Aim 'rmemn connut, A conronarroN orImaw You.

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muoltlon lied' Ilich 5, 1931, lclill lv This invention relates totransmission sys. tems and more particularly to a method of and meansfor providing secrecy in the transmission of messages ovei` suchsystems.

In general it is the object of the invention to rovide a Asystem ofcommunication over which messages, such for example astelephonic-messages, ma be transmitted in such a manner that it w' lbepractically impossible for unauthorized persons who might have accessto the medium through -or over which the messages are transmitted toobtain the 'information "contained therein. It is furthermorea feature4of the arrangements of the invention that they are applicable .both tosystems of communication employing metallic conductors as the medium oftransmission and to radio systems. Other objects and features of theinvention will appear more fully from the detailed descriptionhereinafter given.

In the arrangements of this invention the message currents are renderedunintelligible at the sendin station by distortion and are transmitted,in such unintelligible form to the receiving station. At the receivingstation the incoming distorted message currents 'are given acompensating or -restoring distortion and thus Jrestored to intelligibleform. The ori al distortion and restoring distortion ma accomplished byany suit- 'able electrica device lwhich has a nonlinear operating curve.Such a device, for urposes of illustration, mi ht lbe the we knownvacuum tube ampl' er.. The distorting device at the sending station willbe adjusted to operatemon a portion of its operating curve which has anon-linear characteristic, thereby distorting and rendering the messa ecurrents uninte ligible. The device at te receiving station will beadjusted to-operate on a ortion of its operating curve which is compementa to the rtion of the curve selected for t e o ration of the`distorting device at the sendmg station. In this manner the messagecurrents may be restored a to' an intelligible form'at the receivingstation'. The invention .may be more fully understood Ifrom th'efollowing description `when n. Maeva. aenewsa 0mm a, im.

read in connection with f the accompanyin i drawing, in the Figures 1,2, 3 and 4 o which are illustrated the arrangements thereof. Figs. 1 and2 are graphical illustrations of the operating characteristics of thedistorting and redistorting devices respectively. In Fig. 3 are shownschematically the arrangements ofthe invention as applied to a one-waytwo wire line, while in Fig. 4 is illustrated how the arrangements mightbe embodied in a two-way circuit. Similar reference characters have beenutilized to denote like parts in all of th/e figures of the drawing.

Asy has been pointed out the vacuunrtube amplifier is an electricaldevice having a nonlinear operating characteristic suitable for thearran ements of this invention. In Figs. 1 and 2 t ere is illustratedgraphically the curve 7 which is the operating curve of the vacuum'tube, or more specifically the inputvo1tageoutputcurrent curve. It willbe seen that this curve has non-linear characteristics near the lowerand upper `parts of the curve and substantially linearl characteristics.near the central portion of the curve illustrated. Accordingly thedistorting tube at the sendngstation will be adjusted to operate ona'non-linear portion of the curve such as the lower portion. The effectof this will be seen from a comparison of the wave forms 3 and 4. As themessage current, especially in the case of telephone currents, iscomposed of a lurality of frequencies and is of a complex orm, theinvention is illustrated b taking a wave form representing one of esecomponent frequencies and accordin l the wave forms 3 and 4 are of simpe to function. It will now be seen from the dotted line that the waveform 4. is composed i sulciently distorted to be rendered uninadjustedto function on a non-linear portionwhich are deemed desirable, it isunder.

Kelli 'ble.

e tube at the receiving statlon will be of the operating` curve, such asthe upper portion of the curve, which, is complementary to the portionof the curve on which the tube at the sending station functions. Theresult will then be as' illustrated by the wave forms and 6. `The waveform 5 shows the applied input volta e -rom the current of the wave form4, which as hasbeen pointed out is in distorted and unintelligible form.The wave' form 6 will represent the output current which will resultunder these conditions due ,to the non-linear operatin characteristic atwhich the tube) is adjuste to function. It Will'be seen that the waveform 6 is composed of variations of equal amplitude and 1s similar towaveform 3. In other words the distortion, as shown b wave forms 4 and5, will be removed and til restored to its original and intelligibleform.

In Fig. 3 the arrangements of the invention are showgi i'n a one-waytransmission line. In this arrangement the original message currents aretransmitted over a section L of the transmission line to the. distortingdevice 1, by which they are rendered unintelligible. The message inunintelligible formation will then be transmitted to the receivingstation over a channel, such" as L1, lt is pointed out that the channelL, might be a wire line or the messages might be transmitted to thereceiving station by wireless methods and apparatus if desired. At thereceiving station the messagesxin unintelligible formation would betransmitted through the restoring device 2 and thus restored tointelligible formation and thence transmitted over section L2 of theline to any suitable re-y ceiving apparatus. The distoter 1 vat thesendin station would operate in accordance with t e graphicalrepresentations of Fig.

1 and the restorer -2 would operate in ac cordance with the graphicalrepresentations of Fig. 2. It is pointed out that the devices 1 and 2are not limited to vacuum tube amplifiers, but may be any suitableelectrical devices .which have non-linear operating characteristics.

t In Fig. 4 the arrangements of the invention are shown in atwoway-ztransmission line. At each station in this type of line therewould be provided the hybrid windings 9 and 10 and the balancin networksN, and N2, and the hybrid win such as 11 and 12, and the networks, lsucas N, and N4. At each station there would be proe message current otherthan those illustrated. Accordingly,l while the arrangements have beenillustrated,

as embodied in certain specific arrangements stood that they are capableof embodiment in many and widely varied forms without departing from thespirit of the invention as delined in the appended claims.

What is claimed is:

1. The method of providing secrec in a system of communication whichconsists in translating original message currents mto a current wavewhose elements bear a non- It is linear `i'elation to the correspondingelements of the original message currents, transmitting Ithe -translatedwave to a recelving station, and subjecting the -received wave' at saidstation to a non-linear translation complementary to the translation atthe send'- ing station whereby the, message currents .will be restoredto original formation.

l2. A transmission system including a sending station and a receiving)station, a transmitting channel at said sending station, a device insaid transmitting channel having -a voltage-current operating curveportions of which are non-linear, said device being adjusted to operateon one of the non-linear portions of said curve to distort said messagecurrentsin the same frequency range as the original messagecurrent'sfmeans or transmitting said message currents Ito said receivingstation in'said distorted condition, a receiving channel at saidreceivin station, a rdevice insaid receiving channel aving avoltage-current operatinggcurve similar to the operating curve of saiddevice at said vsending station, said device at said receiving stationbeing adjusted to operate on a nonlinear portion of its curve whichcom-` plementary to the portion ofthe curve on'.

which said -device at s'aid sending station operates to remove thedistortion from said received message currents torender themintelligible.

- 3. A transmission system including a sending station and a receivingstati n, a trans. mlttmg channel -at said sending station, a

vacuum bulb device in said transmitting channel having an in ut-vo'ltageoutput-current curve portions o .which have non-linear 1characteristics,saidv vacuum bulb bein --ad'- justed to `operate on one ofthe non-hnearportions of said curve to distort the message currents in the samefrequency rangeI as the original message currents, means fortransmitting said distorted message currents to said receiving station,a receiving channel at said receivmg station, a vacuum bulb denewness` il B' vice in said receiving c-,hannel having an device atsaid sendingstation operates to input-voltage output-current curve similar removethe distortion from said received to the curve of said" device at saidsending message currents to render them intelli ble. 10 station, saiddevice at said receivingistation In testimony whereof, I havelsi ne my vbeing adjusted to operate one non-linear name tov this specificationthis 2n day of portlon of its curve which `is complementary Mai-cli,1921. V-

to the portion` of the curve on which said LLOYD ESPENSCHED.

